Conventional wireless telecommunication networks, such as cellular and digital wireless telephony networks, create a geographically large coverage area through the use of base stations, antennas (e.g., Node-B and Base Transceiver Station cell towers), Mobile Switching Centers (MSCs), and other equipment common to wireless telecommunication network infrastructure deployments. Conventional network infrastructure provides geographically large coverage areas capable of supporting large numbers of simultaneous communication sessions with mobile devices.
In some situations, it may be desirable for a telephony service provider operating such a network to deploy wireless base stations that are capable of establishing comparatively small network coverage areas. The wireless base stations are less sophisticated and less costly devices that are typically designed to provide wireless telephone network coverage to a few mobile devices (e.g., 4 to 6 simultaneous mobile devices) rather than the large numbers (e.g., 100+ simultaneous mobile devices) provided by a conventional network telecommunications system. The coverage area of the wireless base stations is also designed to be small compared with that of conventional network infrastructure, for example, limited to the size of a home or an office versus a coverage area of several densely populated city blocks, or rural coverage expanding over potentially hundreds of acres. The small coverage areas established by such base stations may be referred to as “femto cells.”
Femto cells and their corresponding base stations (often referred to as Femto Cell Base Stations or Home Node-Bs (HNBs)) are commonly deployed by telephony network providers and are designed to operate with the same mobile devices that operate within a larger wireless telecommunications network. For example, a telephony service provider operating a GSM (Global System for Mobile communications) network, will design the base stations to operate with GSM compatible mobile devices. Similar to conventional network base stations, femto cell base stations broadcast a pilot signal that, when encountered by a compatible mobile device, can trigger the mobile device to connect with the femto cell base station, and consequently, disconnect from a nearby base station, in what is referred to as a “handoff.”
Handoffs between network base stations (conventional or otherwise) are intentionally designed to be imperceptible to the mobile device being handed off, or to end users of such devices. However, in some wireless telephony applications, it may be desirable for mobile devices to be notified of a successful handoff to another base station, such as a short-range femto cell base station. Notification may be desirable for a variety of reasons, but generally speaking the use of a femto cell benefits end users via improved signal quality, enhanced network services, and potentially reduced fees when operating within a femto cell. Telephony service providers also benefit from use of femto cell technology by way of reduced network load on a corresponding conventional network. Accordingly, notifying end users of femto cell use is beneficial to telephony service providers and end-users alike.
Unfortunately, conventional mechanisms for notifying a mobile device of its entry or exit from a femto cell coverage area are insufficient. Some base stations hardware manufacturers transmit a tone or a beep to mobile devices within the femto cell coverage area by decompressing the audio stream sent to the mobile device, inserting the tone or beep by either mixing it with the audio stream to produce a combination of the notification tone and the audio stream, or blocking out the audio stream and substituting the tone in place of the audio stream, and re-compressing the audio stream for transmission to the mobile device during the time period of the notification tone playback. While such a technique is feasible, it requires costly hardware and processing capabilities to decompress and recompress the compressed audio stream quickly enough to avoid perceptible audio delays or content loss at the mobile device. Sophisticated decompression and compression processing power is a costly addition to an otherwise low-cost device, and when multiplied over thousands of units, the costs may become overly burdensome to a service provider who otherwise desires to deploy femto cell technology. Adding near real time compression and decompression capabilities to a femto cell base station may become so cost prohibitive to a service provider looking to scale-up a deployment program, that the entire technology becomes economically infeasible.